I have this intermittant noise that seems to come from under the dash near or in the brake pedal/master cylinder. When I depress the pedal it makes a chattering/squeaking noise.

I looked under the dash to see where the noise is coming from and possibly grease some linkage. The noise sounds like it's coming from inside a rubber boot the is connected to the firewall (master cylinder?).

Is this something I should be worried about? Should I replace this? Can I get in the rubber boot and spray some white grease?

Any help is greatly appreciated.

I don't know the answer to this question, but I can attest to your situation. My '00 brake pedal also squeaks as I press it / release it. It almost has a pneumatic sound to it too, as if I am stepping on a cat lung or something. I haven't really had a chance to diagnose it yet, but I'd be interested to hear of your findings. All I can say is that it went away and now it's back since I degreased my engine compartment. So I thought it was an interior grease point issue, but now I'm a little concerned.

It hasn't made the noise for some time. The last time it was making noise I looked under the dash and could not see anything to grease/lubricate because the noise doesn't come from the linkage.

Stepping on a cat lung, eh? To come up with such a graphic correlation can only represent repetetive instances occuring in the presance of an enlightened and imaginative mind. Love it man.
Sounds like the pushrod from the pedal where it contacts the recess in the brake booster (under the gator boot) may need some lithium lube shot in with a can and straw.
Had a guy with a squeek in his clutch pedal once. Checked everything, lubed fulcrums, couldn't replicate his complaint. Turns out the noise was coming from his marachi sandals as his foot bent to release the clutch.